Effects in Dogs of Decrease in Glomerular Filtration Rate on Cation Excretion During Intravenous Administration of Unreabsorbable Anions

¹ From the Department of Physiology, Cornell University Medical College, New York City

Glomerular filtration rate (GFR) was reduced in stages (by inflation of a balloon located in the aorta above the renal arteries) during administration of the Na salts of the ‘unreabsorbable’ anions, p-aminohippurate or thiosulfate. The large excretion of anions obligated equivalent excretion of cations. The fraction of excreted anions neutralized by Na ions decreased as GFR was reduced; the fraction neutralized by K, NH₄ and H ions increased correspondingly. The ‘availability’ of these three cations was apparently limited so that, at any given level of GFR, the larger the total anion excretion the smaller was the fraction neutralized by these cations. Substitution of K, NH₄ and H for Na was presumably accomplished by ion exchange mechanisms. Net ‘secretion’ of K was demonstrated with increasing frequency as GFR was reduced below 60% of control. Absolute excretions of K, NH₄ and H ions remained within control ranges until GFR decreased below about 50% of control. Absolute excretion of Na, however, decreased sharply with decrease in GFR. It is concluded that acute reduction of GFR, by itself, results in a more complete absorption of filtered sodium; if in this circumstance unreabsorbed anions in tubular fluid obligate cation excretion a considerable proportion of the cations, as K, NH₄ and H ions, are provided by the tubule cells in exchange for some of the reabsorbed Na ions.